Microwave-excited light emitting device

ABSTRACT

A microwave-excited light emitting device is provided comprising an electrodeless evacuated discharge lamp containing ionizable elements and mounted in the frequency determining resonator of a microwave oscillator. The oscillator resonator is tuned to provide a microwave frequency of sufficiently high frequency to provide ionization and excitation of the elements within the electrodeless discharge lamp while mitigating deterious ion bombardment of the walls of the electrodeless discharge lamp. By placing the lamp in the oscillator resonator any changes in the electrical characteristics of the lamp after firing will cause a frequency change in the oscillator allowing the lamp and the oscillator to remain in tuned relationship. However, the oscillator is further provided with thermal isolation means to isolate the lamp from the active device within the oscillator such as a vacuum tube or a solid state device. The light-emitting device is further provided with heating means to conduct externally generated heat to the lamp thermally independently of the active device. In this manner the lamp may be operated at a steady, and preferably elevated, temperature without exposing the active device to excessive heat which would have a deleterious effect on the life of the active device.

United States Patent 1191 Bolin et al.

[111 I 3,790,852 [451 Fees, 1974 [5 1 MICROWAVE-EXCITED LIGHT EMITTINGDEVICE [75] Inventors: Larry R. Bolin; Claude Hopper, .lr.,

both of Owensboro, Ky.; Shelby A. Jolly, Rockport, Ind.

[73] Assignee: General Electric Company,

Owensboro, Ky.

[22] Filed: Apr. 28, 1972 [21] Appl. No.: 248,478

Primary Examiner-John Kominski Attorney, Agent, or FirmNathan J.Cornfeld; Dennis A. Dearing; Frank L. Neuhauser [57] ABSTRACT Amicrowave-excited light emitting device is provided comprising anelectrodeless evacuated discharge lamp containing ionizable elements andmounted in the frequency determining resonator of a microwaveoscillator. The oscillator resonator is tuned to provide a microwavefrequency of sufficiently high frequency to provide ionization andexcitation of the elements within the electrodeless discharge-lamp whilemitigating deterious ion bombardment of the'walls of the electrodelessdischarge lamp. By placing the lamp in the oscillator resonator anychanges in the electrical characteristics of the lamp after firing willcause a frequency change in the oscillator allowing the lamp and theoscillator to remain in tuned relationship. However, the oscillator isfurther provided with thermal isolation means to isolate the lamp fromthe active device within the oscillator such as a vacuum tube or a solidstate device. The light-emitting device is further provided with heatingmeans to conduct externally generated heat to the lamp thermallyindependently of the active device. In this manner the lamp may beoperated at a steady, and preferably elevated, temperature withoutexposing the active device to excessive heat which would have adeleterious effect on the life of the active device.

9 Claims, 1 Drawing Figure MICROWAVE-EXCITED LIGHT EMITTING DEVICECROSS-REFERENCE TO RELATED APPLICATION This application is related to U.S. patent application, Ser. No. 248,477 (G. E. Docket No. 36-08-0598)filed concurrently in the names of L. R. Bolin and S. A. Jolly andassigned to the assignee of the invention herein.

BACKGROUND OF THE INVENTION This invention relates to light-emittingdevices excited to emit light by electromagnetic energy of microwavewavelength. More particularly, this invention relates to a microwavedevice comprising a microwave cavity oscillator having a liht emittingelectrodeless lamp integrally mounted therein and thermally isolatedfrom the active device within the oscillator.

In certain types of apparatus, such as, for example, spectroscopicanalysis equipment for the identification of the presence of certainelements in samples, a modulated beam of a light spectrum of the elementin question is produced to excite the sample. This modulated lightsource has been produced using hollow cathode electron dischargedevices. However, for certain elements this has proved unsatisfactorybecause the presence of the particular element shortens the life of thehollow cathode.

It has therefore been proposed to produce the desired light spectrum byexciting such elements using microwaves. The element is encapsulated,together with an inert gas, in an electrodeless lamp comprising a sealedenvelope transparent to the desired wavelengths of light, such as, forexample, quartz or other glasses. The lamp is placed in a microwavecavity resonator in the particular location desired for light emissionand coupled to a microwave cavity oscillator resonator to provide thepower source for the excitation.

However, it has been found that at low frequencies, i.e., lower thanabout 500 mHz, the excited ions within the lamp bombard the glassenvelope of the lamp with the resultant undesirable shortening of lamplife. At higher frequencies this problem is mitigated or eliminatedbutother problems are encountered which are thought to be due to anuntuned condition between the two cavity resonators housing,respectively, the ocsillator and the lamp. This is apparently due to thelamp cavity resonator resonating a different frequency when the lamp isin an unexcited or unfired state than when the elements are excited. Inthe aforementioned patent application of Bolin and Jolly this problem issolved by placing the electrodeless discharge lamp in the same resonatorwhich determines the frequency of the oscillator. Thus, changes in theelectrical characteristics of the lamp which occur after firing willresult in a frequency shift in the oscillator which allows the lamp andthe oscillator to remain in tuned relationship.

However, it has been further found that it is desirable to operate theelectrodeless discharge lamp at a given temperature which is usuallyhotter than that normally found in the oscillator. Normally thetemperature in the oscillator will fluctuate due to warmup of the activedevice or the like. Also the presence of elevated temperatures, whiledesirable for the operation of the electrodeless discharge lamp, may bedeleterious to the active device thereby shortening its life.

It is therefore an object of the invention to provide an integral,microwave stimulated, light-emitting device comprising a microwaveoscillator cavity resonator containing an electrodeless light-emittinglamp which is thermally isolated from the active device in theoscillator. It is another object of the invention to provide means forstabilizing the temperature of the electrodeless discharge lamp. It isyet another object of the invention to provide supplemental heatingmeans to raise the operating temperature of the electrodeless dischargelamp. These and other objects of the invention will be apparent from thefollowing description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING The sole drawing of the invention is apartially cutaway cross-sectional view of the oscillator.

DESCRIPTION OF THE INVENTION The invention generally comprises a lightemitting device comprising a microwave oscillator generally indicated at2 having a composite outer electrically conductive shell comprisingshell sections 6, 8, and 10 and containing an electrodeless dischargelamp 60 adjacent one end thereof, an active device 30 adjacent anopposite end, and means therebetween comprising a resonant cavitygenerally indicated at numeral 40 which cooperated with the activedevice 30 to provide an oscillator to provide a sustained emission ofmicrowave energy at the resonant frequency of the device as determinedby the various parameters of the associated circurt.

Shell section 10 comprises a hollow metal shell which may be providedwith a cylindrical bore therein. A metal end cap 12 is fitted into thecentral bore in shell 10 to provide an end wall 12 therein. End wall 12,in turn, communicates with a hollow metal tube 14 and a larger diametermetal tube 16 within shell 10 to electrically couple end wall 12 with acathode terminal 32 of active device 30 which, in the illustratedembodiment, comprises a triode electron discharge device having theusual cathode, grid, and anode electrodes (not shown). Heater wires forthe cathode are connected by leads 34 to terminal 17 and 18 on end wall12. Terminal 17 is grounded to the end wall 12 while terminal 18 isbrought out through an insulator 19.

Device 30 is also provided with a grid terminal ring 38 which isconnected to a metallic grid cylinder 44 having a dielectric coatingthereon to insulate it from shell 10. The grid of device 30 is connectedto a terminal 24 via a lead 22 in grid resistor 23 leading from the gridcylinder 44. Terminal 24 is mounted in end wall 12 and insulatedtherefrom by an insulator 25.

Device 30 has an anode stud 36 thereon which is coupled to an anode linecomprising solid cylinder member 46 and hollow sleeve member 48 whichwill be described in more detail below. Power is supplied to anode stud36 through a terminal 50 mounted to end wall 12 and insulated therefromby an insulator S2. A lead wire 54 connected to cylinder member 46passes through a shield 55 to terminal 50 through an RF choke 58.

Feedback fingers 15 electrically connnected to the cathode 32 passthrough openings in the end wall of grid cylinder 44 feed energy fromthe plate surface back to the cathode surface to sustain oscillation ofthe device.

The oscillator provides microwave energy in a manner well known to thoseskilled in the art and described, for example, in Chapter 6 ofElectronic Designers Handbook; by R. W. Lande, D. C. Davis, and A. P.Albrecht; McGraw-l-lill Book Company, Inc.; 1957.

As previously mentioned above, anode stud 36 is coupled to an anode linecomprising a solid cylinder or cylindrical member 46 and a hollowcylinder 48. Cylinder or rod 46 is threadedly secured to stud 36 andcomprises a copper or aluminum or other good heat conducting andelectrical conducting material. Sleeve 48 is then connected as by athreaded or press fit to a reduced end portion of cylinder 46. Sleeve 48comprises a cylinder of poor heat conducting material such as, forexample, lnvar. Cylinder 48 is plated with copper or other suitablemetal to provide good electrical-characteristics.

Surrounding cylinder 46 is a sleeve 72 of good heat conducting andelectrically insulating material such as beryllia. Sleeve 72 has acentral bore therein approximately the same diameter as cylinder 46 toinsure a tight fit to provide a good thermal coupling therebetween. Theouter diameter of sleeve 72 is approximately the same as the innerdiameter of shell 10 to, in turn, provide good thermal couplingtherebetween. Heat generated by active device 30, particularly adjacentthe anode portion, is thereby connected through cylinder 46 and sleeve72 to the outer shell 10 from whence it may be dissipated to thesurrounding environment.

As previously stated, the outer shell of the oscillator is a compositecomprising shell portions 6, 8, and 10. Shell portion 6, like shellportion 10, comprises a good heat conducting metal having a cylindricalbore therein. Shell portion 6 is separated from shell portion 10 by anintermediate shell 8 which is constructed of, for example, lnvar orother poor heat conducting material plated with copper or other suitablematerial to provide good electrical materials. The adjoining ends of therespective shell portions may be suitably joined together by threadedconnections, press fitting, or metallurgical bonding.

Electrodeless discharge lamp 60 comprises a sealed, hollow ampulecomprising silica or glass or the like and containing gas of theparticular elements, for example, mercury vapor, and inert gas such asargon. The lamp 60 is mounted, in the illustrated embodiment, in acentral bore of a sleeve 74 which is constructed of a good heatconducting material such as beryllia. Sleeve 74, in turn, has anexternal dimension matching the internal configuration of shell 6 sothat it may be tightly fitted therein in good thermal communicationtherewith.

Sleeve 48 of the anode line is dimensioned to extend toward theelectrodeless discharge lamp 60 mounted in sleeve 74 so that the narrowend 62 of lamp 60 fits within the end of sleeve 48. The length of theanode line and the length of shell 8 are dimensioned to be,electrically, one-half wavelength long, taking into account theforeshortening of the capacitance at the anode end of the anode line.Thus, the electrodeless discharge lamp 60 is placed approximately in aposition of maximum electrical field strength. This is desirable toprovide maximum intensity of the field and therefore maximum brillianceof the emitted light resulting from the excitation from the ions withinthe lamp by the microwave energy. Slight adjustments, of course, of theposition of lamp 60 to provide the maximum impedance matching of thelamp to the anode line may be necessary to provide the most efficientoperation.

In the illustrated embodiment, an end wall 13 is also provided on theend of the oscillator shell 6. End wall 13 has a central window 1321which provides a columnated beam of light from the electrodelessdischarge lamp. It should be noted, however, that this is not necessaryfor the operation of the device but may be preferred for certain uses.

In a preferred embodiment, shell 6 is surrounded by a heater coil whichis capable of supplying additional heat to the electrodeless dischargelamp through thermal conduction via shell 6 and sleeve 74. in thismanner the lamp may be heated to a preselected temperature above thenormal operating temperature of the oscillator and then maintained atthat temperature.

The device operates by initiation of oscillation between the cavityresonator and the amplifier means at a preselected frequency. Microwaveenergy generated thereby is transmitted to the electrodeless dischargelamp whereby the ions therein are excited to emit light therefrom. Thesustained emission oflight based on excitation of the vapor or gastherein can result in a frequency shift in the oscillator. While thiseffect is not fully understood, it is believed to be the result of achange in the impedance of the load resulting from a change in thereactance of the lamp under excitation conditions as opposed to theunexcited state. These changes in reactance change the resonantfrequency of the cavity which, in turn, results in the shift infrequency of the oscillator. This frequency shift, however, affects boththe oscillator and the lamp. Hence, the oscillator and the lamp remainin a tuned condition resulting in maximum efficiency of operation.

However, due to the construction of shell 8 and anode line portion 48 ofpoor heat conducting material, the oscillator, although electricallyfunctioning as an integral device, is thermally isolated into two shellchambers, the shell chamber housing active device 30 adjacent shellportion 10 and the chamber housing electrodeless discharge lamp 60adjacent shell portion 6. Each of these chambers comprises an outershell portion (10-6) of good heat conducting material, a sleeve ofinsulating material which is a good heat conductor, and a central devicefrom which heat is either conducted toward or away from. In this mannerthe electrodeless discharge lamp may be operated at a temperaturepreselected for maximum efficiency of the lamp. The active device, onthe other hand, may be operated at a reduced temperature with any heatgenerated from the device being conducted to the outer shell 10 anddissipated to the atmosphere thereby providing a lower operatingtemperature for the active device resulting in longer life.

Thus, the invention provides an integral device wherein an electrodelessdischarge lamp is mounted in the frequency determinating resonator of amicrowave oscillator, yet is thermally isolated from the active devicein the oscillator. While the invention has been described with regard toa particular configuration and particular materials it should be readilyapparent that minor modifications as well as substitutions of othermaterials having similar properties may be made without departing fromthe scope of the invention which is to be limited only by the appendedclaims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A light-emitting device comprising:

a. a microwave oscillator including:

1. 'a composite electrically conductive shell defining a resonantcavity, said conductive shell being dimensioned to be electricallyone-half the operating frequency wavelength, and thus creating at leasttwo positions of maximum electric field intensity;

2. an active device disposed within said cavity adjacent one of said atleast two positions for providing asustained emission of microwaveenergy at a predetermined operating frequency;

b. an electrodeless discharge lamp disposed within said cavity andspaced from said active means at least a distance one-half the operatingfrequency wavelength of said cavity and thereby being disposed ofanother of said at least two positions of maximum electric intensity insaid cavity;

c. a first heat transmitting means, interposed between said activedevice and said lamp, for conducting heat generated by the active deviceto the surrounding environment, said first heat transmitting means beingconstructed of an electrically nonconductive material.

2. The device of claim 1 wherein said shell comprises a first shellportion adjacent said active device, having good heat conductingproperties, said first shell portion being thermally coupled to saidfirst heat transmitting means; a second shell portion adjacent saidlamp, havinggood heat conducting properties; and a third shell portioninterposed between said first and second members, having poor thermalconducting properties.

3. The device of claim 2 wherein said oscillator fur- 'ther comprises acentral electrode having a first portion electrically coupled to saidactive device and a second portion comprising a poor thermal conductorextending from said first portion toward said lamp, said centralelectrode first portion extending through and being thermally coupled tosaid first heat-transmitting means.

4. The light-emitting device of claim 3 wherein said lamp is disposed insaid second portion of said central electrode and a second heattransmitting means is thermally coupled between said lamp and saidsecond portion of said shell for conducting heat to and away from saidlamp, said second heat transmitting means being constructed of anelectrically non-conductive material.

5. The light-emitting device of claim 4 wherein heat generating means isthermally coupled to said second shell portion.

6. A light-emitting device comprising:

a. a microwave oscillator including:

1. a composite electrically conductive shell defining a resonant cavity,said conductive shell dimensioned to be electrically one-half theoperating frequency wavelength and thus creating at least two positionsof maximum electric field intensity;

2. means dividing said resonant cavity into first and second shellchambers;

3. an active device, disposed within said first shell chamber, adjacentone of said at least two positions for providing a sustained emission ofmicrowave energy at a predetermined operating frequency;

b. an electrodeless discharge lamp disposed within said second shellchamber and spaced from said active means at least a distance one-halfthe operating frequency wavelength of said cavity and thereby beingdisposed at another of said at least two positions.

7. The device of claim 6 wherein said shell comprises a first shellportion having good heat conductive properties, said first shell portiondefining said first shell chamber, and a second shell portion havinggood heat conducting properties, said second shell portion defining saidsecond shell chamber; and said dividing means includes a first heattransmitting means thermally coupled to said first shell portion fortransmitting heat generated by the active device to said first shellportion for dissipation to the surrounding environment and a second heattransmitting means thermally coupled between said lamp and said secondshell portion for conducting heat to and away from said lamp, said firstand second heat transmitting means constructed of electricallynon-conductive material. 8. The device of claim 7 wherein said shellfurther comprises a third shell portion interposed between said firstand second shell portions having poor thermal conducting properties.

9. The device of claim 7 wherein heat generating means is thermallycoupled to said second shell por- UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patmfl1No. 3,790,852 Datai February 5, 1974Invmumr(s) Larry R. Bolin; Claude Hopper, Jr.; Shelby A. Jolly It iscertified that error appears in the above-identified patefit and thatsaid Letters Patent are hereby corrected as shown below:

Column 5, Claim 1, Line 17, cancel "of" (first occurrence) and insertat.

Signed and sealed this 10th day of September 197h."

v (SEAL) I Attestz v 'MccoY M. GIBSON; JR; 0. MARSHALL DANN AttestingOfficer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC 60376-P69i: use sovzrgunsflfgnmrms orncs: Isa d-ase-au I I

1. A light-emitting device comprising: a. a microwave oscillatorincluding:
 1. a composite electrically conductive shell defining aresonant cavity, said conductive shell being dimensioned to beelectrically one-half the operating frequency wavelength, and thuscreating at least two positions of maximum electric field intensity; 2.an active device disposed within said cavity adjacent one of said atleast two positions for providing a sustained emission of microwaveenergy at a predetermined operaTing frequency; b. an electrodelessdischarge lamp disposed within said cavity and spaced from said activemeans at least a distance one-half the operating frequency wavelength ofsaid cavity and thereby being disposed of another of said at least twopositions of maximum electric intensity in said cavity; c. a first heattransmitting means, interposed between said active device and said lamp,for conducting heat generated by the active device to the surroundingenvironment, said first heat transmitting means being constructed of anelectrically non-conductive material.
 2. The device of claim 1 whereinsaid shell comprises a first shell portion adjacent said active device,having good heat conducting properties, said first shell portion beingthermally coupled to said first heat transmitting means; a second shellportion adjacent said lamp, having good heat conducting properties; anda third shell portion interposed between said first and second members,having poor thermal conducting properties.
 2. an active device disposedwithin said cavity adjacent one of said at least two positions forproviding a sustained emission of microwave energy at a predeterminedoperaTing frequency; b. an electrodeless discharge lamp disposed withinsaid cavity and spaced from said active means at least a distanceone-half the operating frequency wavelength of said cavity and therebybeing disposed of another of said at least two positions of maximumelectric intensity in said cavity; c. a first heat transmitting means,interposed between said active device and said lamp, for conducting heatgenerated by the active device to the surrounding environment, saidfirst heat transmitting means being constructed of an electricallynon-conductive material.
 2. means dividing said resonant cavity intofirst and second shell chambers;
 3. an active device, disposed withinsaid first shell chamber, adjacent one of said at least two positionsfor providing a sustained emission of microwave energy at apredetermined operating frequency; b. an electrodeless discharge lampdisposed within said second shell chamber and spaced from said activemeans at least a distance one-half the operating frequency wavelength ofsaid cavity and thereby being disposed at another of said at least twopositions.
 3. The device of claim 2 wherein said oscillator furthercomprises a central electrode having a first portion electricallycoupled to said active device and a second portion comprising a poorthermal conductor extending from said first portion toward said lamp,said central electrode first portion extending through and beingthermally coupled to said first heat-transmitting means.
 4. Thelight-emitting device of claim 3 wherein said lamp is disposed in saidsecond portion of said central electrode and a second heat transmittingmeans is thermally coupled between said lamp and said second portion ofsaid shell for conducting heat to and away from said lamp, said secondheat transmitting means being constructed of an electricallynon-conductive material.
 5. The light-emitting device of claim 4 whereinheat generating means is thermally coupled to said second shell portion.6. A light-emitting device comprising: a. a microwave oscillatorincluding:
 7. The device of claim 6 wherein said shell comprises a firstshell portion having good heat conductive properties, said first shellportion defining said first shell chamber, and a second shell portionhaving good heat conducting properties, said second shell portiondefining said second shell chamber; and said dividing means includes afirst heat transmitting means thermally coupled to said first shellportion for transmitting heat generated by the active device to saidfirst shell portion for dissipation to the surrounding environment and asecond heat transmitting means thermally coupled between said lamp andsaid second shell portion for conducting heat to and away from saidlamp, said first and second heat transmitting means constructed ofelectrically non-conductive material.
 8. The device of claim 7 whereinsaid shell further comprises a third shell portion interposed betweensaid first and second shell portions having poor thermal conductingproperties.
 9. The device of claim 7 wherein heat generating means isthermally coupled to said second shell portion.